Use of fire to heat the interior of a structure is one of the oldest practices known to man. One of the earliest refinements of this practice took place in Europe in the fifteenth century: the introduction of a flue or chimney so that the heated, rising air would draw smoke out of the structure.
The present conventional fireplace still utilizes a flue or chimney, which is often mounted in an exterior wall of the heated structure. Wall mounting of the fireplace and chimney requires the use of bricks, masonry, or other insulating materials to prevent damage to the wall.
For a number of reasons, the conventional wall mounted, masonry, fireplace is impractical for use in smaller structures such as mobile homes. The heat insulating material required for protection of walls would add cumbersome weight to the structure. Also, in a mobile home, where space is at a premium, the mere size of the conventional fireplace is a hindrance to its installation and use. Furthermore, movement of combusted gases out of the structure through the chimney creates a partial vacuum within the structure. To replace the oxygen burned up in the firebox, cold outside air must then leak into the structure, causing drafts around doors and windows. Smaller structures are especially susceptible to this problem.
Attempts have been made to use air flow over a fireplace firebox to reduce or eliminate the need for masonry. See, for example, U.S. Pat. Np. 2,821,975 to Thulman, granted Feb. 4, 1958, in which air enters an outer chamber at the top of the smokestack, flows downward and around the fireplace, and leaves through an inner chamber surrounding the stack. This tends to cool the outside surface of the fireplace, reducing the need for heat insulating materials. The technique is also seen in U.S. Pat. No. 3,601,117 to Carson, granted Aug. 24, 1971.
There have been attempts to increase the efficiency of the conventional fireplace by generating a flow of heated air into the room. U.S. Pat. No. 3,190,279 to Davis, granted on June 22, 1965, shows room air entering a chamber below the firebox, proceeding upward in the chamber along the sides of the firebox, and finally flowing back into the room. Of course, this will not counteract the tendency of combustion to form a partial vacuum within the structure, and does not provide replacement oxygen.
Attempts to solve the vacuum problem are seen in U.S. Pat. No. 3,094,980 to Inabnit granted on June 25, 1963, and in U.S. Pat. No. 3,096,754 to Howrey, granted July 9, 1963. Inabnit utilizes fans to draw air downward through a chamber which surrounds the smokestack, and into the structure. This air will tend to cool the stack, become heated due to its proximity to the stack, and consequently tend to heat the room when it is released to the room. In Howrey, air enters from the room into a chamber surrounding the firebox and is expelled back into the room, thereby serving a dual purpose of cooling the exterior surface of the firebox and heating the room. In addition, combustion air may be supplied through an auxiliary line which connects the firebox directly to the outside of the structure. Thus, the principal use shown for outside air is to supply oxygen for combustion.